Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Sea-Bird Dissolved Oxygen Sensor SBE 43 and SBE 43F

The SBE 43 is a dissolved oxygen sensor designed for marine applications. It incorporates a high-performance Clark polarographic membrane with a pump that continuously plumbs water through it, preventing algal growth and the development of anoxic conditions when the sensor is taking measurements.

Two configurations are available: SBE 43 produces a voltage output and can be incorporated with any Sea-Bird CTD that accepts input from a 0-5 volt auxiliary sensor, while the SBE 43F produces a frequency output and can be integrated with an SBE 52-MP (Moored Profiler CTD) or used for OEM applications. The specifications below are common to both.

Instrument Description

CTD Unit and Auxiliary Sensors

A Sea-Bird Electronics SBE 911 plus CTD unit was used. Water samples were collected using a Sea-Bird SBE35 carousel. The CTD unit included the following sensors.

Sensor

Manufacturer

Model

Serial number

Calibration date

Pressure

Paroscientific

Digiquartz

64240

2009-06-30

Temperature

Sea-Bird

SBE3

2041

2008-07-10

Conductivity

Sea-Bird

SBE4

1615

2008-07-23

Temperature

Sea-Bird

SBE3

2105

2008-07-10

Conductivity

Sea-Bird

SBE4

1669

2008-06-27

Oxygen

Sea-Bird

SBE43

0504

2009-06-23

Fluorometer

Wet Labs

ECO_FL

FLRTD-064

2003-11-08

Transmissometer

Wet Labs

C-Star

CST-704DR

2003-08-25

Sea-Bird Electronics SBE 911 and SBE 917 series CTD profilers

The SBE 911 and SBE 917 series of conductivity-temperature-depth (CTD) units are used to collect hydrographic profiles, including temperature, conductivity and pressure as standard. Each profiler consists of an underwater unit and deck unit or SEARAM. Auxiliary sensors, such as fluorometers, dissolved oxygen sensors and transmissometers, and carousel water samplers are commonly added to the underwater unit.

Underwater unit

The CTD underwater unit (SBE 9 or SBE 9 plus ) comprises a protective cage (usually with a carousel water sampler), including a main pressure housing containing power supplies, acquisition electronics, telemetry circuitry, and a suite of modular sensors. The original SBE 9 incorporated Sea-Bird's standard modular SBE 3 temperature sensor and SBE 4 conductivity sensor, and a Paroscientific Digiquartz pressure sensor. The conductivity cell was connected to a pump-fed plastic tubing circuit that could include auxiliary sensors. Each SBE 9 unit was custom built to individual specification. The SBE 9 was replaced in 1997 by an off-the-shelf version, termed the SBE 9 plus , that incorporated the SBE 3 plus (or SBE 3P) temperature sensor, SBE 4C conductivity sensor and a Paroscientific Digiquartz pressure sensor. Sensors could be connected to a pump-fed plastic tubing circuit or stand-alone.

Temperature, conductivity and pressure sensors

The conductivity, temperature, and pressure sensors supplied with Sea-Bird CTD systems have outputs in the form of variable frequencies, which are measured using high-speed parallel counters. The resulting count totals are converted to numeric representations of the original frequencies, which bear a direct relationship to temperature, conductivity or pressure. Sampling frequencies for these sensors are typically set at 24 Hz.

The temperature sensing element is a glass-coated thermistor bead, pressure-protected inside a stainless steel tube, while the conductivity sensing element is a cylindrical, flow-through, borosilicate glass cell with three internal platinum electrodes. Thermistor resistance or conductivity cell resistance, respectively, is the controlling element in an optimized Wien Bridge oscillator circuit, which produces a frequency output that can be converted to a temperature or conductivity reading. These sensors are available with depth ratings of 6800 m (aluminium housing) or 10500 m (titanium housing). The Paroscientific Digiquartz pressure sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

Additional sensors

Optional sensors for dissolved oxygen, pH, light transmission, fluorescence and others do not require the very high levels of resolution needed in the primary CTD channels, nor do these sensors generally offer variable frequency outputs. Accordingly, signals from the auxiliary sensors are acquired using a conventional voltage-input multiplexed A/D converter (optional). Some Sea-Bird CTDs use a strain gauge pressure sensor (Senso-Metrics) in which case their pressure output data is in the same form as that from the auxiliary sensors as described above.

Deck unit or SEARAM

Each underwater unit is connected to a power supply and data logging system: the SBE 11 (or SBE 11 plus ) deck unit allows real-time interfacing between the deck and the underwater unit via a conductive wire, while the submersible SBE 17 (or SBE 17 plus ) SEARAM plugs directly into the underwater unit and data are downloaded on recovery of the CTD. The combination of SBE 9 and SBE 17 or SBE 11 are termed SBE 917 or SBE 911, respectively, while the combinations of SBE 9 plus and SBE 17 plus or SBE 11 plus are termed SBE 917 plus or SBE 911 plus .

WETLabs ECO FLNTU fluorescence and turbidity sensor

The Environmental Characterization Optics (ECO) Fluorometer and Turbidity (FLNTU) sensor is a dual wavelength, single-angle instrument that simultaneously determines chlorophyll fluorescence and turbidity. It is easily integrated in CTD packages and provides a reliable turbidity measurement that is not affected by Colored Dissolved Organic Matter (CDOM) concentration.

The FLNTU can operate continuously or periodically and has two different types of connectors to output the data. There are 5 other models that operate the same way as this instrument but have slight differences, as stated below:

FLNTU(RT) - has an analog an RS-232 serial output and operates continuously, when power is supplied

FLNTU(RT)D - similar to the FLNTU(RT) but has a depth rating of 6000 m

FLNTUB - has internal batteries for autonomous operation

FLNTUS - has an integrated anti-fouling bio-wiper

FLNTUSB - has the same characteristics as the FLNTUS but with internal batteries for autonomous operation

Paroscientific Absolute Pressure Transducers Series 3000 and 4000

Paroscientific Series 3000 and 4000 pressure transducers use a Digiquartz pressure sensor to provide high accuracy and precision data. The sensor comprises a quartz crystal resonator that responds to pressure-induced stress, and temperature is measured for thermal compensation of the calculated pressure.

The 3000 series of transducers includes one model, the 31K-101, whereas the 4000 series includes several models, listed in the table below. All transducers exhibit repeatability of better than ±0.01% full pressure scale, hysteresis of better than ±0.02% full scale and acceleration sensitivity of ±0.008% full scale /g (three axis average). Pressure resolution is better than 0.0001% and accuracy is typically 0.01% over a broad range of temperatures.

Differences between the models lie in their pressure and operating temperature ranges, as detailed below:

WETLabs C-Star transmissometer

This instrument is designed to measure beam transmittance by submersion or with an optional flow tube for pumped applications. It can be used in profiles, moorings or as part of an underway system.

Two models are available, a 25 cm pathlength, which can be built in aluminum or co-polymer, and a 10 cm pathlength with a plastic housing. Both have an analog output, but a digital model is also available.

This instrument has been updated to provide a high resolution RS232 data output, while maintaining the same design and characteristics.

BODC Processing

Data were received by BODC in one ASCII format file that was subsequently split into 131 separate files, one for each CTD profile. The series were reformatted to the internal BODC format. Sample calibrations were applied to the conductivity data. The following table details mapping of variables to BODC parameter codes.

Original parameter name

Original Units

Description

BODC Parameter Code

BODC Units

Comments

Pressure

Decibars

Pressure (spatial co-ordinate) exerted by the water body by profiling pressure sensor and corrected to read zero at sea level

PRESPR01

Decibars

Temperature

°C

Temperature of the water body by CTD or STD

TEMPST01

°C

Conductivity

mS cm -1

Electrical conductivity of the water body by in-situ conductivity cell and calibration against independent measurements

CNCLCCI1

S m -1

Conversion by transfer (mS cm -1 x 0.1). Sample calibrations applied.

Salinity

Practical salinity of the water body by CTD and computation using UNESCO 1983 algorithm and calibration against independent measurements

PSALCC01

Dimensionless

Derived by transfer using UNESCO 1983 algorithm

Fluorescence

µg l -1

Concentration of chlorophyll-a {chl-a} per unit volume of the water body [particulate phase] by in-situ chlorophyll fluorometer and calibration against sample data

CPHLPS01

mg m -3

Sample calibrations applied.

Beam Attenuation

Volts

Attenuance (red light wavelength) per unit length of the water body by 20 or 25cm path length transmissometer

ATTNMR01

m -1

Oxygen

cm 3 dm -3

Concentration of oxygen {O2} per unit volume of the water body [dissolved phase] by Sea-Bird SBE 43 sensor and no calibration against sample data

DOXYSU01

µmol l -1

Unit conversion (x44.66) applied

Oxygen Saturation

%

Saturation of oxygen {O2} in the water body [dissolved phase]

OXYSZZ01

%

Following transfer to QXF, the data were screened using BODC's in-house visualisation software. Any data considered as suspect were flagged.

Originator's Data Processing

Sampling Strategy

A total of 131 CTD casts were performed on FRV Scotia cruise 0610S (14 May 2010 - 1 June 2010) in the North Sea and north east Atlantic Ocean - in particular East Shetland, Faroe-Shetland Channel and Fair Isle Channel. The data were collected between 15:10 hours GMT on 14 May 2010 and 11:31 hours GMT on 31 May 2010.

Water samples were collected in order to obtain independent salinity measurements. The sample data were used to derive calibrations for the conductivity and fluorescence profiles collected by the CTD.

Data Processing

The raw CTD data files were processed through the SeaBird Electronics SeaSoft data processing software following standard procedures. The originators used in-house interactive visual display editing software to edit out individual spikes in the primary temperature and conductivity channels. In addition, a low-pass filter (Sy, 1985) was applied to particularly noisy data. An ASCII file was generated for each CTD cast and all files from a cruise were concatenated into one ASCII file which was submitted to BODC.

Field Calibrations

Independent salinity samples, obtained from the sample bottle and spread throughout the cruise, were used to calibrate the CTD conductivity and fluoresence data. Outlying points were discarded, and between 121 and 125 data points were used to derive the calibrations. The sample analyses yielded a straight line conductivity calibration of the form y = mx + c, where m=1.000150 and c = 0.003027, and a straight line fluoresence calibration of the form y = mx +c, where m=0.005259 and c=-0.323648.

Parameter

Value of m (y=mx+c)

Value of c (y=mx+c)

Equation

Conductivity

1.000150

0.003027

C(cal) = 1.000150C(obs) + 0.003027

Fluoresence

0.005259

-0.323648

C(cal) = 0.005259C(obs) - 0.323648

The uncalibrated data and calibrations were submitted to BODC, who applied the appropriate corrections.